Semiconductor device for improving electrical and mechanical connectivity of conductive pillers and method therefor

ABSTRACT

A semiconductor device has a semiconductor die having a first surface and a second surface wherein at least one bond pad is formed on the first surface. A passivation layer is formed on the first surface of the semiconductor device, wherein a central area of the at least one bond is exposed. A seed layer is formed on exposed portions of the bond pad and the passivation layer. A conductive pillar is formed on the seed layer. The conductive pillar has a base portion wherein the base portion has a diameter smaller than the seed layer and a stress relief portion extending from a lateral surface of a lower section of the base portion toward distal ends of the seed layer. A solder layer is formed on the conductive pillar.

FIELD OF THE INVENTION

This invention relates to a semiconductor device and, more specifically, to a semiconductor device having conductive pillars with a stress relief portion that reduces stresses generated at ends of contact portions between the conductive pillar and a seed layer to prevent the conductive pillar and the seed layer from being disconnected from each other due to stress.

BACKGROUND OF THE INVENTION

Semiconductor devices having a chip scale package (CSP) structure are typically manufactured such that after the manufacturing process has been accomplished, a finished wafer is singulated as individual semiconductor chips. In recent years, a flip chip semiconductor device has been developed as a semiconductor having a CSP structure. A flip chip semiconductor device is manufactured by forming a conductive bump having a predetermined height on a bond pad of a semiconductor die, and may be electrically connected to an external device like a printed circuit board through the conductive bump.

However, contact portions between distal ends of a conductive bump and a semiconductor die is vulnerable to external forces. Thus, the conductive bump may be subject to considerable stresses. In such a case, electrical and mechanical properties of the flip chip semiconductor device may deteriorate.

Therefore, a need existed to provide a system and method to overcome the above problem.

SUMMARY OF THE INVENTION

A semiconductor device has a semiconductor die having a first surface and a second surface wherein at least one bond pad is formed on the first surface. A passivation layer is formed on the first surface of the semiconductor device, wherein a central area of the at least one bond is exposed. A seed layer is formed on exposed portions of the bond pad and the passivation layer. A conductive pillar is formed on the seed layer. The conductive pillar has a base portion wherein the base portion has a diameter smaller than the seed layer and a stress relief portion extending from a lateral surface of a lower section of the base portion toward distal ends of the seed layer. A solder layer is formed on the conductive pillar.

A method for manufacturing a semiconductor device, comprising: forming a passivation layer on a first surface of a semiconductor die having at least one bond pad, wherein a central area of the at least one bond pad is exposed; forming a seed layer on the passivation layer and exposed portions of the at least one bond pad; forming a photoresist layer on the seed layer; forming a first through hole and a second through hole, the first through hole formed on the photoresist layer to expose a portion of the seed layer corresponding to a region including the bond pad, and the second through hole extending from a lateral surface of a lower portion of the first through hole toward the photoresist layer; forming a conductive pillar by filling the through hole with a conductive material; forming a solder layer on the conductive pillar; and removing the photoresist layer and portions of the seed layer.

The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating a semiconductor device according to an embodiment of the present invention;

FIG. 2 is a flowchart showing a method for manufacturing a semiconductor device according to an embodiment of the present invention; and

FIGS. 3A through 3H are sectional views sequentially illustrating various process steps of the manufacturing method of the semiconductor device illustrated in FIG. 2.

Common reference numerals are used throughout the drawings and detailed description to indicate like elements.

DETAILED DESCRIPTION

Referring to FIG. 1, a semiconductor device 100 according to an embodiment of the present invention is shown. The semiconductor device 100 may include a semiconductor die 110, a seed layer 120, a conductive pillar 150, and a solder layer 160.

The semiconductor die 110 may be made of silicon, and may include a first surface 110 a, and a second surface 110 b that is substantially planar and opposite to the first surface 110 a. The semiconductor die 110 may also include at least one bond pad 111 formed on the first surface 110 a. The bond pad 111 may be used to send an electrical signal input and or output to and or from the semiconductor die 110. The bond pad 11 may be electrically coupled to an active region (not shown) of the semiconductor die 110. The bond pad 111 may be made of aluminum. However, the bond pad 111 is not limited thereto and may be formed of other materials without departing from the spirit and scope of the present invention.

The semiconductor die 110 may further include a passivation layer 112 formed on a portion of the first surface 110 a. In general, the passivation layer 112 is not applied over a central area of the bond pad 111. However, the passivation layer 112 may be formed over an outer periphery of the bond pad 111. The passivation layer 112 may be made of any one selected from an oxide layer (SiO₂), a nitride layer (Si₃N₄), equivalents thereof, but aspects of the present invention are not limited thereto.

The seed layer 120 may be formed between the bond pad 111 and the passivation layer 112. As shown in FIG. 1, the seed layer 120 is applied on the exposed areas of the bond pad 11 and over portions of the passivation layer 112 around an outer perimeter of the bond pad 111. The seed layer 120 may be made of at least one selected from the group consisting of titanium (Ti), copper (Cu), nickel (Ni), gold (Au), silver (Ag), aluminum (Al), and equivalents thereof, but aspects of the present invention may not be limited thereto. The seed layer 120 allows the conductive pillar 140 to be plated and firmly attached to the passivation layer 112.

The conductive pillar 150 is formed on the seed layer 120 to a predetermined height. The conductive pillar 150 is a conductive protrusion for connecting the semiconductor device 100 to an external device, such as a printed circuit board, and serves as a bump. In detail, the conductive pillar 150 includes a base portion 151 and a stress relief portion 152.

The base portion 151 has a smaller diameter than the seed layer 120, and plays a main part in electrically connecting the semiconductor die 110 to an external device, such as a printed circuit board.

The stress relief portion 152 is formed as a protrusion extending from the lateral surface of a lower portion of the base portion 151 toward distal ends of the seed layer 120. The stress relief portion 152 relieves stresses applied to contact portions between the conductive pillar 150 and the seed layer 120. Here, the stress relief portion 152 may be formed to have a height gradually decreasing from the lateral surface of the lower portion of the base portion 151 toward the distal ends of the seed layer 120. In addition, the distal ends of the stress relief portion 152 and the distal ends of the seed layer 120 may coincide with each other. A length of the stress relief portion 152 extending from the lateral surface of the base portion 151 may be in a range of 0.1 μm˜3 μm, which is suitable for relieving the stresses applied to the distal ends of the contact portions between the conductive pillar 150 and the seed layer 120.

The conductive pillar 150 may include the base portion 151 and the stress relief portion 152 integrally formed with each other, and may be made of at least one selected from the group consisting of copper (Cu), nickel (Ni), gold (Au), silver (Ag), aluminum (Al), and equivalents thereof, but aspects of the present invention may not be limited thereto.

The solder layer 160 is fusibly attached onto the conductive pillar in a substantially spherical shape. The solder layer 160 may transfer electrical signals to and or from the semiconductor die 110 and an external circuit such as a printed circuit board. The solder layer 160 may be made of at least one selected from the group consisting of Sn—Pb, Sn—Pb—Ag, Sn—Pb—Bi, Sn—Cu, Sn—Ag, Sn—Bi, Sn—Ag—Cu, Sn—Ag—Bi, Sn—Zn, and equivalents thereof, but aspects of the present invention are not limited thereto.

As described above, the semiconductor device 100 according to an embodiment of the present invention includes the conductive pillar 150 with the stress relief portion 152, thereby reducing stresses generated at ends of contact portions between the conductive pillar 150 and the seed layer 120. Therefore, the semiconductor device 100 can prevent the conductive pillar 150 and the seed layer 120 from being disconnected from each other due to stress, thereby preventing electrical and mechanical properties thereof from deteriorating.

Referring to FIG. 2, a flowchart for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention is illustrated. Referring to FIGS. 3A through 3H, sectional views of various process steps of the manufacturing method of the semiconductor device illustrated in FIG. 2 are sequentially illustrated.

As illustrated in FIG. 2, the method for manufacturing the semiconductor device 100 according to an embodiment of the present invention includes preparing a semiconductor die (S1), forming a seed layer and a photoresist layer (S2), forming a through hole (S3), forming a conductive pillar and a solder layer (S4), and removing a photoresist layer and a seed layer (S5).

As illustrated in FIG. 3A, in the preparing of the semiconductor die (S1), the semiconductor die 110 having a first surface 110 a that is substantially planar, and a second surface 110 b that is substantially planar and opposite to the first surface 110 a is prepared, the first surface 110 a having at least one bond pad 111 formed thereon. Here, a passivation layer 112 is formed on the first surface 110 a excluding a central region corresponding to the bond pad 111. As shown, the passivation layer 112 may cover the outer perimeter of the bond pad 111.

As illustrated in FIGS. 3B and 3C, in the forming of the seed layer 120 and the photoresist layer 130 (S2), the seed layer 120 having a predetermined thickness is formed on the bond pad 111 and the passivation layer 112, and the photoresist layer 130 having a predetermined thickness is then formed on the seed layer 120.

The seed layer 120 may be formed by blanket depositing at least one selected from the group consisting of titanium (Ti), copper (Cu), nickel (Ni), gold (Au), silver (Ag), aluminum (Al), and equivalents thereof, on the bond pad 111 and the passivation layer 112, by sputtering, chemical vapor deposition (CVD), or plasma enhanced chemical vapor deposition (PECVD). However, the seed layer 120 may be formed in other manners without departing from the spirit and scope of the present invention.

The photoresist layer 130 may be formed by adhering a dry film resist to an entire surface of the seed layer 120 by lamination. The dry film resist may be formed by coating a photoresist material on a polyethylene terephthalate (PET) film and adhering a polyethylene (PE) film thereon. The dry film resist may be used for forming high-density, high-integration circuit patterns. The photoresist layer 130 may be formed by other means without departing from the spirit and scope of the present invention.

As illustrated in FIG. 3D, in the forming of the through hole (S3), the through hole 140 may include a first through hole 141 and a second through hole 142 is formed on the photoresist layer 130. The through hole 140 may be formed by sequentially performing steps of exposing, developing and baking on the photoresist layer 130. Other means may be used to form the first and second through hole 141 and 142 without departing from the spirit and scope of the present invention.

The first through hole 141 may be formed to expose a region of the seed layer 120 corresponding to the region including the bond pad 111. In detail, the first through hole 141 may be formed by removing a non-exposed region (NER) of the photoresist layer 130, except for an exposed region (ER) of the photoresist layer 130. To this end, the dry film resist used to form the photoresist layer 130 may be a negative-type photoresist. Here, the exposed region (ER) is a region that is exposed to light, while the non-exposed region (NER) is a region that is not exposed to light during the exposing step of the photoresist layer 130. The non-exposed region (NER) is removed using a developing solution during the developing step.

The second through hole 142 may be formed such that it extends from a lateral surface of the lower portion of the first through hole 141 toward the photoresist layer 130. In detail, the second through hole 142 may be formed by additionally removing a partial portion of the exposed region (ER) of the photoresist layer 130 using a developing solution during the developing step, the partial portion being barely exposed to light (that is, the partial portion is a portion where the non-exposed region (NER) and the exposed region (ER) contact with each other in a surface of the seed layer 120).

In accordance with one embodiment, in the exposing step for forming the first through hole 141 and the second through hole 142, the exposed region (ER) of the photoresist layer 130 is exposed to a dose of 30 to 50% of a normal exposure dose for completely transforming the property of the photoresist layer 130. This is to allow the exposed region (ER) of the photoresist layer 130 to be exposed to light to a low dose so that a portion of the exposed region (ER) of the photoresist layer 130 is barely exposed to light. That is to say, the portion of the exposed region (ER) of the photoresist layer 130 that is barely exposed to light is made to be removed by a development solution, thereby forming the second through hole 142. Here, if the exposed region (ER) of the photoresist layer 130 is exposed to a dose of less than 30% that of normal exposure, exposure of the exposed region (ER) of the photoresist layer 130 is not sufficient, most of the exposed region (ER) of the photoresist layer 130 may be undesirably removed during the developing step using the developing solution. If the exposed region (ER) of the photoresist layer 130 is exposed to a dose of greater than 50% that of normal exposure, the cost of the exposing step for forming the second through hole 142 may be greatly increased.

In order to form a through hole on a dry film resist, it is common to sequentially perform exposing, baking and developing steps. In the exemplary embodiment of the present invention, however, in order to facilitate formation of the second through hole 142, the exposing, developing and baking steps are sequentially performed in that order. This is because if the developing step, prior to the baking step is performed in a state in which adhesion of the dry film resist is weak, then the partial portion of the exposed region (ER) of the photoresist layer 130 for forming the second through hole 142 can be more efficiently removed.

As illustrated in FIGS. 3E and 3F, in the forming of the conductive pillar and the solder layer (S4), the conductive pillar 150 and the solder layer 160 are formed in the through hole 140. The conductive pillar 150 may be formed by filling the through hole 140 with a conductive material by, for example, plating. The conductive pillar 150 may include a base portion 151 formed in the first through hole 141, and a stress relief portion 152 formed in the second through hole 142. A top surface of the base portion 151 may be lower than that of the photoresist layer 130, by which a space in which the solder layer 160 is formed can be provided inside the through hole 140.

The solder layer 160 is formed on the conductive pillar 150 inside the through hole 140, by, for example, plating. As illustrated in FIG. 3G, in the removing of the photoresist layer and the seed layer (S5), the photoresist layer 130 is completely removed and the seed layer 120 is partially removed. The removing of the photoresist layer 130 may be performed by, for example, stripping. The removing of the seed layer 120 may be performed by, for example, etching. Here, the etching may be performed such that the distal ends of the stress relief portion 152 and the distal ends of the seed layer 120 may coincide with each other. In the removing of the seed layer 120, the stress relief portion 152 may serve as a barrier preventing an overetching of the seed layer 120, thereby preventing the seed layer 120 from caving in toward the base portion 151.

Following the removing of the photoresist layer and the seed layer (S5), the solder layer 160 is reflowed. The reflowing allows the solder layer 160 to be fusibly attached onto the conductive pillar 150 in a substantially spherical shape, as illustrated in FIG. 3H.

This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure. 

1. A semiconductor device comprising: a semiconductor die having a first surface and a second surface, at least one bond pad formed on the first surface; a passivation layer formed on the first surface of the semiconductor device, wherein a central area of the at least one bond is exposed; a seed layer formed on exposed portions of the bond pad and the passivation layer; a conductive pillar formed on the seed layer, the conductive pillar comprising: a base portion, the base portion having diameter smaller than a maximum diameter of the seed layer; and a stress relief portion extending from a lateral surface of a lower section of the base portion toward distal ends of the seed layer, wherein the base portion and the stress relief portion are formed of a same material; and a solder layer formed on the conductive pillar.
 2. The semiconductor device of claim 1, wherein the base portion and the stress relief portion are integrally formed.
 3. The semiconductor device of claim 1, wherein the stress relief portion has a height gradually decreasing from the lateral surface of the lower portion of the base portion toward the distal ends of the seed layer.
 4. The semiconductor device of claim 1, wherein distal ends of the stress relief portion covers the distal ends of the seed layer.
 5. The semiconductor device of claim 1, wherein a length of the stress relief portion extending from the lateral surface of the lower section of the base portion toward the distal ends of the seed layer is in a range of 0.1 μm to 3 μm.
 6. The semiconductor device of claim 1, wherein the conductive pillar is made of at least one of copper (Cu), nickel (Ni), gold (Au), silver (Ag), aluminum (Al), and combinations thereof.
 7. The semiconductor device of claim 1, wherein the solder layer is in contact with a top surface of the base portion.
 8. A semiconductor device comprising: a semiconductor die having a first surface and a second surface, at least one bond pad formed on the first surface; a passivation layer formed on the first surface of the semiconductor device, wherein a central area of the at least one bond is exposed; a seed layer formed on exposed portions of the bond pad and the passivation layer; a conductive pillar formed on the seed layer, the conductive pillar comprising: a base portion, the base portion having diameter smaller than a maximum diameter of the seed layer; and means extending from the lateral surface of a lower section of the base portion toward distal ends of the seed layer for reducing stresses generated at ends of contact portions between the conductive pillar and the seed layer, wherein the base portion and the means for reducing stresses are formed of a same material; and a solder layer formed on the conductive pillar.
 9. The semiconductor device of claim 8, wherein the base portion and the means for reducing stresses are integrally formed.
 10. The semiconductor device of claim 8, wherein the means for reducing stresses has a height gradually decreasing from the lateral surface of the lower portion of the base portion toward the distal ends of the seed layer.
 11. The semiconductor device of claim 8, wherein distal ends of the means for reducing stresses cover the distal ends of the seed layer.
 12. The semiconductor device of claim 8, wherein a length of the means for reducing stresses extend from the lateral surface of the lower section of the base portion toward the distal ends of the seed layer is in a range of 0.1 μm to 3 μm.
 13. The semiconductor device of claim 8, wherein the conductive pillar is made of at least one of copper (Cu), nickel (Ni), gold (Au), silver (Ag), aluminum (Al), and combinations thereof.
 14. The semiconductor device of claim 8, wherein the solder layer is in contact with a top surface of the base portion.
 15. A semiconductor device comprising: a semiconductor die having at least one bond pad formed thereon; a seed layer formed on exposed portions of the bond pad; a conductive pillar formed on the seed layer, the conductive pillar comprising: a base portion, the base portion having diameter smaller than a maximum diameter of the seed layer; and a stress relief portion extending from a lateral surface of a lower section of the base portion toward distal ends of the seed layer, wherein the base portion and the stress relief portion are formed of a same material; and a solder layer formed on the conductive pillar.
 16. The semiconductor device of claim 15 further comprising a passivation layer formed on the semiconductor device, wherein a central area of the at least one bond is exposed.
 17. The semiconductor device of claim 15, wherein the base portion and the stress relief portion are integrally formed.
 18. The semiconductor device of claim 15, wherein the stress relief portion has a height gradually decreasing from the lateral surface of the lower portion of the base portion toward the distal ends of the seed layer.
 19. The semiconductor device of claim 15, wherein distal ends of the stress relief portion covers the distal ends of the seed layer.
 20. The semiconductor device of claim 15, wherein the solder layer is in contact with a top surface of the base portion. 